The organic light emitting diode (OLED) is an example of a material that is produced by coating multiple layers of different materials on a substrate. The canonical OLED structure includes a cathode (C), a hole transport layer (HTL), an emissive layer (EL), an electron transport layer (ETL), and an anode (A). This structure is presented as C-HTL-EL-ETL-A. This canonical structure represents a simplification of the more complex structures that have evolved as OLED devices and manufacture have become more sophisticated. However, for the purposes of this invention, using this simplified description makes description and understanding of the invention easer. For more specific examples of device structure in which a subset of the device layers are repeated, see for example, in Liao et al., U.S. Pat. No. 6,717,358. In these recently disclosed devices, the somewhat simplified representation of the structure has the form C-(HTL-EL-ETL)n-A, where the notation ( . . . )n indicates that the group inside the parentheses can be repeated two or more times. This class of device structures, which are referred to as a stacked OLED, is important because it provides increased device efficiency at a relatively modest cost in device complexity.
A number of disclosures have proposed strategies for the making of OLED devices on flexible substrates by utilizing web-based coating systems, for example, in Kakinuma, U.S. Pat. No. 6,579,422. In a web-based system, a flexible substrate is moved past stationary deposition sources using a variety of ways that are common in web transport systems, such as rollers, drums, tensioning devices, etc. In previously disclosed systems it is necessary to provide a coating station containing the deposition sources for each layer of the OLED being produced. As a consequence, making of a device such as the stacked OLED requires an additional set of coating sources for each copy of the repeated group in the stack. This is a severe drawback for two reasons. First, it is expensive to replicate the sources, both in initial capital and on-going operational cost. Second, the resulting system can only be used with great difficulty and waste to make devices with a smaller number of replications in the stack.